Flexible printing plate locking device



Dec. 25, 1956 c cLAFF ET AL 2,775,199

FLEXIBLE PRINTING PLATE LOCKING DEVICE Filed Feb. 24, 1953 Fig. I I5INVENTORS CLARENCE LLOYD CLAFF CARL A. MOELLER ATTORNEYS r 2,775,199FLEXIBLE PRINTING PLATE LOCKING DEVICE Clarence Lloyd Clafi' and Carl A.Moeller, Randolph, Mass., assignors, by mesne assignments, to M. B.Clalf & Sons, Inc., Randolph, Mass., a corporation .of MassachusettsApplication February 24, 1953, Serial No. 338,338

1 Claim. (Cl. 101-4151) The present invention relates to lithographicprinting presses, duplicating machines, and the like, and moreparticularly to an improved device for securing a flexible lithographicplate or other sheet printing means to the surface of the platecylinder.

A lithographic plate consists, essentially, of a base material orsupport and a coating on a surface of the support adapted to be preparedfor selective wetting by a printing ink. A considerable variety of basematerials may be used. in the case of rotary lithographic presses it .isnecessary that such materials be deformable into a cylindrical shape.This permits the image to be transferred to the coating while thesupport is flattened in a plane, as in the case of photolithography, orwrapped upon a radius differing from that of the plate roll or cylinder,as in the case of typewritten lithographic printing. The support maythen be wrapped upon the cylinder and securedthereto by its ends. Inusual practice, the surface of the plate cylinder is relieved to form aslot running parallel to the axis of rotation, and means are provided tosecure the ends of the support within the The specific form and mode ofoperation of the plate securing means depend to a considerable extentupon the selection of the base material. The relevant properties of thismaterial include its stifiness and elasticity as respects bending orfolding, and its strength and resistance to tearing. These and otherproperties, as will be understood by those familiar with this art,determine the amount, if any, of circumferential stretching force to beapplied to insure a smooth, fiat fit upon the cylinder. They alsodetermine the means to be used in gripping the ends of the plate,whether for example by screws, by bolts or rivets, by jaws or clamps ofone type or another, by frictional devices, or by some combination ofthese or other suitable means.

It is a principal object of the present invention to provide an improvedplate securing device, especially, although not exclusively, adapted forsecuring relatively thin fiexibleplates having base materials consistingof paper, plastic, cloth, or similar materials, characterized byflexibility and relatively low tear strength.

gins to form a resilient filler structure for frictionally binding theends of the lithographic plate Within the slot.

The invention is further characterized by a construction which permitsthe plate locking device to be inserted Withinthe slot in the platecylinder in a manner facilitating the removal of folds and wrinkles inthe plate, as well as even distribution of the clamping forces actingupon the ends of the plate.

Other features Will be evident from the following description of thepreferred embodiment, taken in conjunction with the drawings, in which:

Fig. 1 is an end view of a plate cylinder with the novel plate securingdevice in place, taken in a plane perpendicular to the axis of thecylinder.

Fig. 2 is an oblique view of the plate securing device.

Fig. 3 is a sectional view of a portion of the plate cylinder at theslot, taken on the line 3-3 of Fig. l and showing the locking device inoperative position.

Referring to Fig. l, the plate cylinder 4 is constructed in any desiredmanner, being mounted for rotation about the axis of a shaft 5, and hasa more or less continuous cylindrical surface, with a depression or slotrunning parallel to its axis. The sides 6 of the slot are preferablyrounded very slightly, as shown in the drawing, at the intersectionbetween the slot and the cylinder periphery. Also, the cylinderperiphery adjacent the slot on each side is relieved very slightly for ashort distance, to permit the portion of the plate in the vicinity ofthe slot to lie a slight distance radially inward from the periphery ofthe main portion of the plate, for a purpose hereinafter described.

As a further object, the plate securing device should be of simpledesign, suitable for rapid mounting and removal of the plate with aminimum of effort, yet so constructed as to insure a consistently smoothand wrinklefree fit of the plate upon the surface of the cylinder.

A further object is to provide means for adjusting the securing devicefor various thicknesses of base material, such as different weights ofpaper, as well as to insure an even distribution of the gripping forcealong the margins of the material within the slot.

With these objects in view, a principal feature of this inventionresides in a plate-locking device of laminated construction consistingof two strips of rigid material separated by a layer of rubber orrubber-like material, with adjustable means for drawing the stripstogether to cause the rubber to protrude at the longitudinal mar- Theplate 8, when in secured position, is wrapped around the cylinder withits ends projecting into the slot toward, but preferably not reaching,the bottom of the slot. It is effectively secured in this positionfrictionally by the plate securing device, which presses each end ormargin of the plate against a wall of the slot.

The construction of a preferred form of the securing device is showngenerally in Fig. 2. The device comprises spaced strips 10 and 12 ofrigid material, preferably but not necessarily metal, with a strip 14 ofrubber or rubber-like material interposed between the strips andprojecting slightly beyond the longitudinal margins of the strips. Thebottom strip 12 is preferably provided with a notch 16 at one end forengagement under the head of a screw 18 threaded into the cylinder 4.The width of the strip is slightly less than the clearance in the slotwith the plate 8 in position as shown in Fig. 1. Its length ispreferably somewhat greater than the transverse end dimension of theplate 8. The top strip 10 is of the same width, and preferably ofsubstantially the same length, but associated with the bottom strip inlongitudinally off set relation so as to provide clearance at one endabove the notch 16, while affording a projection 20 at the other end tofacilitate removal from the slot by a prying action with the fingers orother suitable device.

The. two strips are separated by the layer of rubber or rubber-likesubstance 14, which is preferably of the same width as the strips, whenuncompressed. The length of this layer may be the same as, or slightlygreater than, the transverse width of the sheet material to be secured(the lithographic plate). Its preferred thickness is a function of itselastic properties, as well as of the extent by which it is desired toproject or bulge the rubber outwardly to obtain the requisite clampingpressure in the slot.

To secure the sandwich of metal strips and interposed rubber layer,fiat-headed screws 22 pass through unthreaded holes in the strip 10,through the rubber layer 14, and into threaded holes in strip 12. Thesescrews hold the laminae together, and permit the strips 10 and 12 to bedrawn together to bulge the rubber layer so that Patented Dec. 25, 1956V it protrudes the required distance beyond the edges of the strips.They also permit adjustments of the bulge at various points in thelonger dimension, since the strips and 12 are capable offlexure, wherebytheir compressive action on the rubberstrip may be varied from one screwto the next to achieve the desired lateral clamping pressure at anypoint. This is particularly useful in producing an equal distribution ofclamping pressure upon the inturned margins of plate 8, which isimportant where printing plates of low tear strength are employed. Italso facilitates interchangeability of cylinders and plate lockingdevices since, even though variations are encountered in the widths ofthe slots on different plate cylinders, the plate securing device may bequickly adjusted to a proper clamping engagement within the slot.

It will be understood that the number of screws 22 is to be principallydetermined by the choice of rubber or rubber-like material and thethickness and flexibility of the strips 10 and 12. For example, morescrews would be required where the rubber material is extremely stiffand great force is necessary to achieve the req uired protrusion.Similarly, more screws could be used where the rubber material is softif either or both of the strips 10 and 12 is flexible, permittinglocalization of the effect of each individual screw upon the rubberlayer.

As heretofore stated, the structure just described is so adapted as toinsure a consistently smooth and wrinklefree fit of the printing plateupon the surface of the cylinder. To illustrate this feature, theprocedure of mounting a lithographic plate upon the cylinder will nextbe described.

The screws 22 will have been preferably tightened on the basis of aprevious test, in which a test plate, or material of the same thicknessas the plate to be used, is placed in the slot. The test may be soperformed as to ascertain whether the clamping pressure is evenlydistributed. Strips of the plate material may be placed side by side inthe slot, on each side, and each strip may be subjected to a pull todetermine the tension at which it begins to slip out of the securingdevice. Other tests of a more or less complicated nature 'will suggestthemselves to those skilled in this art.

Once the proper adjustments of the screws 22 have been made, alithographic plate may be mounted. The plate is first wrapped around thecylinder, and its ends folded over the edges of the slot. In thisfolding step, the plate may crack. To avoid the possibility of thiscrack picking up ink and transferring it to the blanket roll, thesurface of the cylinder is relieved very slightly on each side of theslot, as described above, to allow such portions of the plate to lieslightly below the active peripheral portions of the plate.

The plate securing device is then inserted in place. First, the securingdevice is held at an acute angle with respect to the slot and the endwith the notch 16 is inserted beneath the head of the screw 18. At thistime, two corners of the plate, one on each end, are held in the slot bythe pressure of short segments of the rubber extending into the slotnear the screw.

The securing device is then pushed into place with a rotary motion aboutthe screw 18. As this is done, the

length of the rubber extending into the slot gradually increases in thedirection away from the screw. Progressively, from one end of thecylinder toward the other, a localized, circumferential, tensioningforce is exerted upon each end of the plate due to the sliding of therubber against the sides of the slot. This force, which issimultaneously applied at each end of the plate, removes the wrinkles inthe plate, starting with the originally fitted side and working towardthe other side. This action is facilitated by the rounded edges of theslot. Thus, the entire plate is drawn into smooth and snug engagementwith the plate cylinder when the securing device reaches its finalposition in the slot.

Removal of the securing device is extremely simple, and involves merelyprying it loose by inserting a finger or suitable tool under theprojecting end 20 of the device lifting upward until the notch end 16 isfree of the screw.

It willbe understood that the invention has been described withreference to a preferred embodiment, and that numerous modifications ofform and details of construction may be incorporated without departingfrom the spirit or scope of the invention. Some of these modificationsare discussed above, and others will occur to those skilled in this artin connection with specific applications.

Having thus described our invention, we claim:

In a rotary printing press, the combination of a plate cylinder having atransverse slot in its surface adapted to receive the inturned ends of aprinting plate of thin flexible material, said slot having substantiallyparallel walls, a projection in one end of the slot, and plate lockingmeans comprising a pair of elongated flexible strips narrower than thewidth of the slot and adapted to be disposed therein with their edgesadjacent the slot walls, resilient material capable of developingfriction with the plate intermediate the said strips, and a number ofindiviually adjustable means spaced along the strips, each of said meansbeing adapted to compress the resilient material between the strips in asubstantially local area to cause the margins of the resilient materialto extend laterally beyond the edges of the strips and thereby toprovide frictional engagement of the inturned ends of the plate againstthe sides of the slot, said plate locking means being adapted to beretained at one end under said projection and to be lowered with arotary motion until it lies in the slot, said resilient materialfrictionally engaging the inturned margins of the printing plate duringsaid rotary motion and thereby exerting a laterally progressivecircumferential pull on the plate around the cylinder.

References Cited in the file of this patent UNITED STATES PATENTS FaeberDec. 16, 1952

